arXiv subjects

Wen-Chen Chang

Publications and source records attributed to Wen-Chen Chang.

At least 19 recordsLinked to original sources

arXiv2026

Determination of charged pion unpolarised TMDPDFs from Drell-Yan measurements

We present an extraction of the unpolarised transverse momentum dependent (TMD) parton distribution functions (PDFs) for the valence quarks in the pion from experimental mea- surements of the Drell-Yan process. The procedure adopted in this project relies on the framework of TMD factorisation, and the inputs of nucleon TMDPDF, pion collinear PDF, as well as the Collins-Soper kernel. The non-perturbative behaviour of the TMDPDFs is parameterised using an ansatz function that contains three unknown parameters and implements an exponential decay at large transverse distances. This work employs the most recent results in perturbation theory, and utilises a precise estimation of the nucleon TMDPDF. We perform an investigation of data used in the fit. This investigation leads to important observations regarding the effects of the kinematics and binning methods in the experimental data. Our results agree qualitatively with the previous determinations from phenomenology and a lattice computation

hep-ph↗

arXiv2026

Leading-Neutron Electroproduction at HERA and the EIC: Sullivan Process, Target Fragmentation, and Pion PDFs

Leading-neutron electroproduction measurements from the H1 and ZEUS experiments at HERA have been used to constrain pion parton distribution functions (PDFs) at small momentum fractions within the Sullivan one-pion-exchange (OPE) framework, complementing large-$x_π$ constraints from pion-induced Drell--Yan measurements. Previous analyses have focused primarily on the region of large neutron longitudinal momentum fraction, $x_L$, where contributions from deep-inelastic scattering (DIS) target fragmentation are suppressed. In this work, we use the \textsc{Pythia} event generator to model the target-fragmentation contribution and show that its combination with the OPE contribution reproduces the main features of the HERA leading-neutron data over the full measured $x_L$ range without introducing additional ad hoc normalization factors. This result demonstrates the potential of incorporating a broader range of leading-neutron data into future global analyses, thereby extending sensitivity to smaller pion momentum fractions $x_π$. We investigate the model dependence associated with the pion--nucleon vertex form factor and show that the HERA data are sensitive to different target-fragmentation treatments implemented in \textsc{Pythia}. Finally, we present projections for leading-neutron production at the future U.S. Electron-Ion Collider (EIC), identifying beam-energy configurations and kinematic regions that provide enhanced sensitivity to pion structure while suppressing DIS target-fragmentation contributions.

hep-ph↗

arXiv2026

Feasibility demonstration of a high-momentum, high-purity muon beamline at the J-PARC Hadron Experimental Facility

We have established and characterized a novel high-purity muon beam delivery scheme, designated as $μ$20, at the high-momentum hadron beamline (B-line) of the J-PARC Hadron Experimental Facility. This scheme delivers tertiary muons produced via the in-flight backward decays of secondary pions in the straight section of the beamline, inherently suppressing parent hadron contamination. In a systematic performance evaluation, the muon beam achieved a standalone intensity of $1.7\times10{^3}$ particles/spill with a spatial spread (standard deviation, $σ$) of approximately 15 mm at the downstream detector position. A systematic attenuation analysis utilizing an iron absorber verified a high muon purity of 98.0$\pm$0.6% for the 3 GeV/$c$ muon beam mode. Crucially, this work marks the first successful feasibility study of a high-momentum and high-purity muon beamline operation at an experimental facility in Japan.

physics.acc-ph↗

arXiv2026

First measurement of $ϕ$ meson production in 30 GeV proton-nucleus reactions via di-electron decay at J-PARC

We present the first measurement of the production of the $ϕ$ meson in 30 GeV proton-nucleus interactions on carbon and copper targets via the di-electron decay channel. The measurement was conducted at the high-momentum beamline of the J-PARC Hadron Experimental Facility, which was commissioned in 2020. The $e^+e^-$ pairs were detected using the E16 spectrometer, during a commissioning run of the J-PARC E16 experiment. The $ϕ$ mesons are successfully reconstructed on all experimental targets. The obtained yields are converted to the total production cross section, assuming a kinematical distribution of the event generator JAM. The total cross sections derived are 2.0 $\pm$ 0.9 (stat.) $\pm$ 1.0 (syst.) mb on the carbon target and 10.3 $\pm$ 4.4 (stat.) $\pm$ 4.4 (syst.) mb on the copper target. The mass-number dependence of the cross section is discussed using the parameter $α$, defined as $σ\propto A^α$, resulting in $α= $ 0.99 $\pm$ 0.38 (stat.) $\pm$ 0.34 (syst.). The extrapolation to $A=1$, which means that the cross section of proton-proton reactions, is in good agreement with the existing measurements at comparable energies.

nucl-ex↗

arXiv2025

Probing Pion Valence Quark Distribution with Beam-charge Asymmetry of Pion-induced $J/ψ$ Production

We consider the beam-charge asymmetry of the $J/ψ$ production cross sections in $π^-$- versus $π^+$-induced reactions on proton or nuclear targets. We show that the $J/ψ$ production cross section difference between $π^-$ and $π^+$ beams impinging on a proton target has a positive sign with a magnitude proportional to the product of pion's valence quark distribution, $V_π$, and proton's up and down valence quark distribution difference, $u^V - d^V$. The existing $J/ψ$ production data for $π^- + p$ and $π^+ + p$ at 39.5 and 200 GeV/c are consistent with the expected positive beam-charge asymmetry. The magnitude of the asymmetry is compared with calculations performed within two theoretical frameworks, the Color Evaporation Model (CEM) and the Non-Relativistic QCD (NRQCD) formalism. We also examine the beam-charge dependence for pion-induced $J/ψ$ production cross sections measured on the neutron-rich platinum target, and find good agreement between the data and theory for both the negative sign and the magnitude of the beam-charge asymmetry. The comparison between data and theoretical calculations for both proton and platinum targets suggests that the beam-charge asymmetry in pion-induced $J/ψ$ production is a viable method of accessing the valence quark distribution of the pion.

hep-ph↗

arXiv2025

Exploring Baryon Resonances with Transition Generalized Parton Distributions: Status and Perspectives

QCD gives rise to a rich spectrum of excited baryon states. Understanding their internal structure is important for many areas of nuclear physics, such as nuclear forces, dense matter, and neutrino-nucleus interactions. Generalized parton distributions (GPDs) are an established tool for characterizing the QCD structure of the ground-state nucleon. They are used to create 3D tomographic images of the quark/gluon structure and quantify the mechanical properties such as the distribution of mass, angular momentum and forces in the system. Transition GPDs extend these concepts to $N \rightarrow N^\ast$ transitions and can be used to characterize the 3D structure and mechanical properties of baryon resonances. They can be probed in high-momentum-transfer exclusive electroproduction processes with resonance transitions $e + N \rightarrow e' + M + N^\ast$, such as deeply-virtual Compton scattering ($M = γ$) or meson production ($M = π, K$, $etc.$), and in related photon/hadron-induced processes. This White Paper describes a research program aiming to explore baryon resonance structure with transition GPDs. This includes the properties and interpretation of the transition GPDs, theoretical methods for structures and processes, first experimental results from JLab 12 GeV, future measurements with existing and planned facilities (JLab detector and energy upgrades, COMPASS/AMBER, EIC, EicC, J-PARC, LHC ultraperihperal collisions), and the theoretical and experimental developments needed to realize this program.

hep-ph↗

arXiv2024

Constraining kaon PDFs from Drell-Yan and $J/ψ$ production

The kaon parton distribution functions (PDFs) are poorly known due to paucity of kaon-induced Drell-Yan data. Nevertheless, these Drell-Yan data suggest a softer valence $u$ quark distribution of kaon than that of pion. We discuss the opportunity to constrain kaon PDFs utilizing existing kaon-induced $J/ψ$ production data. We compare the $K^- / π^-$ and $K^+ / π^+$ cross-section ratio data with calculations based on two global-fit parametrizations and two recent theoretical predictions for the kaon and pion PDFs, and test the results with two quarkonium production models. The $K^- / π^-$ cross-section ratio for $J/ψ$ production provides independent evidence of different valence quark distributions in pion and kaon. The $K^+ / π^+$ $J/ψ$ data are found to be sensitive to the gluon distribution in kaon. We show that these $J/ψ$ production data provide valuable constraints for evaluating the adequacy of currently available sets of kaon PDFs.

hep-ph↗

arXiv2023

Extraction of Kaon Partonic Distribution Functions from Drell-Yan and $J/ψ$ Production Data

We present an analysis to extract kaon parton distribution functions (PDFs) for the first time using meson-induced Drell-Yan and quarkonium production data. Starting from the statistical model first developed for determining the partonic structure of spin-1/2 nucleon and later applied to the spin-0 pion, we have extended this approach to perform a global fit to existing kaon-induced Drell-Yan and $J/ψ$ production data. These data are well described by the statistical model, allowing a first extraction of the kaon PDFs. We find that both the Drell-Yan and the $J/ψ$ data favor a harder valence distribution for strange quark than for up quark in kaon. The kaon gluon distribution is further constrained by the $J/ψ$ production data. In particular, the momentum fraction carried by gluons is found to be similar for pion and kaon.

hep-ph↗

arXiv2023

Pion PDFs confronted by Fixed-Target Charmonium Production

The pion, as the Goldstone boson of the strong interaction, is the lightest QCD bound state and responsible for the long-range nucleon-nucleon interaction inside the nucleus. Our knowledge on the pion partonic structure is limited by the existing Drell-Yan data which are primarily sensitive to the pion valence-quark distributions. The recent progress of global analysis of pion's parton distribution functions (PDFs) utilizing various experimental approaches are introduced. From comparisons between the pion-induced $J/ψ$ and $ψ(2S)$ production data with theoretical calculations using the CEM and NRQCD models, we show how these charmonium production data could provide useful constraints on the pion PDFs.

hep-ph↗

arXiv2023

Fixed-target charmonium production and pion parton distributions

We investigate how charmonium hadroproduction at fixed-target energies can be used to constrain the gluon distribution in pions. Using nonrelativistic QCD (NRQCD) formulation, the $J/ψ$ and $ψ(2S)$ cross sections as a function of longitudinal momentum fraction $x_F$ from pions and protons colliding with light targets, as well as the $ψ(2S)$ to $J/ψ$ cross section ratios, are included in the analysis. The color-octet long-distance matrix elements are found to have a pronounced dependence on the pion parton distribution functions (PDFs). This study shows that the $x_F$ differential cross sections of pion-induced charmonium production impose strong constraints on the pion's quark and gluon PDFs. In particular, the pion PDFs with larger gluon densities provide a significantly better description of the data. It is also found that the production of the $ψ(2S)$ state is associated with a larger quark-antiquark contribution, compared with $J/ψ$.

hep-ph↗

arXiv2022

Pion Partonic Distributions in the Statistical Model from Pion-induced Drell-Yan and $J/Ψ$ Production Data

We present a new analysis to extract pion parton distribution functions (PDFs) within the framework of the statistical model. Starting from the statistical model first developed for the spin-1/2 nucleon, we extend this model to describe the spin-0 pion. Based on a combined fit to both the pion-induced Drell-Yan data and the pion-induced $J/Ψ$ production data, a new set of pion PDFs has been obtained. The inclusion of the $J/Ψ$ production data in the combined fit has provided additional constraints for better determining the gluon distribution in the pion. We also compare the pion PDFs obtained in the statistical model with other existing pion PDFs.

hep-ph↗

arXiv2021

NRQCD analysis of charmonium production with pion and proton beams at fixed-target energies

We present an analysis of hadroproduction of $J/ψ$ and $ψ(2S)$ at fixed-target energies in the framework of non-relativistic QCD (NRQCD). Using both pion- and proton-induced data, a new determination of the color-octet long-distance matrix elements (LDMEs) is obtained. Compared with previous results, the contributions from the $q \bar{q}$ and color-octet processes are significantly enhanced, especially at lower energies. A good agreement between the pion-induced $J/ψ$ production data and NRQCD calculations using the newly obtained LDMEs is achieved. We find that the pion-induced charmonium production data are sensitive to the gluon density of pions, and favor pion PDFs with relatively large gluon contents at large $x$.

hep-ph↗

arXiv2021

Lepton angular distribution of $W$ boson productions

The lepton angular distribution coefficients $A_i$ for $Z$ boson production in $pp$ and $\bar p p$ collisions have been measured at the LHC and the Tevatron. A recent study showed that many features of the measured angular distribution coefficients, including the transverse momentum ($q_T$) and rapidity dependencies and the violation of the Lam-Tung relation, can be well described using an intuitive geometric approach. In this paper, we extend this geometric approach to describe the angular distribution coefficients for $W$ boson produced in $\bar{p} p$ collisions at the Tevatron. We first compare the data with a perturbative QCD calculation at $\mathcal{O}(α_s^2)$. We then show that the data and QCD calculations can be well described with the geometric approach. Implications for future studies at the LHC energy are also discussed.

hep-ph↗

arXiv2021

QCD effects in lepton angular distributions of Drell-Yan/$Z$ production and jet discrimination

We present a comparison of data of lepton angular distributions of Drell-Yan/$Z$ production with the fixed-order pQCD calculations by which the baseline of pQCD effects is illustrated. As for the $Z$ production, we predict that $A_0$ and $A_2$ for $Z$ plus single gluon-jet events are very different from that of $Z$ plus single quark-jet events, allowing a new experimental tool for checking various algorithms which attempt to discriminate quark jets from gluon jets. Using an intuitive geometric approach, we show that the violation of the Lam-Tung relation, appearing at large transverse-momentum region, is attributed to the presence of a non-coplanarity effect. This interpretation is consistent with the appearance of violation beyond LO-QCD effect.

hep-ph↗

arXiv2020

Data acquisition system in Run-0a for the J-PARC E16 experiment

J-PARC E16 is an experiment to examine the origin of hadron mass through a systematic measurement of spectral changes of vector mesons in nuclei. The measurement of $e^{+}e^{-}$ pairs from the decay of vector mesons will provide the information of the partial restoration of the chiral symmetry in a normal nuclear density. To resolve a pulse pile-up and achieve good discrimination of $e^{\pm}$ from the background of a reaction rate of an order of 10 MHz, the data acquisition (DAQ) system uses waveform sampling chips of APV25 and DRS4. The trigger rate and data rate are expected to be 1 kHz and 130--330 MiB/s, respectively. The DAQ system for readout of APV25 and DRS4 were developed, where events were synchronized by common trigger and tag data. The first commissioning in beam, called Run-0a, was performed in June 2020 with about 1/4 of the designed setup. The DAQ worked with a trigger rate of 300 Hz in the Run-0a and the main bottleneck was a large data size of APV25. Further optimization of the DAQ system will improve the performance.

physics.ins-det↗

arXiv2020

Constraining gluon density of pions at large $x$ by pion-induced $J/ψ$ production

The gluon distributions of the pion obtained from various global fits exhibit large variations among them. Within the framework of the color evaporation model, we show that the existing pion-induced $J/ψ$ production data, usually not included in the global fits, can impose useful additional constraints on the pion parton distribution functions (PDFs). In particular, these data can probe the pion's gluon densities at large $x$. Existing pion-induced $J/ψ$ data covering a broad range of beam momenta are compared with next-to-leading-order QCD calculations using various sets of pion PDFs. It is found that $J/ψ$ data measured at forward rapidity and at sufficiently high beam momentum are sensitive to the large-$x$ gluon distribution of pions. The current $J/ψ$ data favor the Sutton-Martin-Roberts-Stirling and Gluck-Reya-Vogt pion PDFs, containing significant gluon content at large $x$.

hep-ph↗

arXiv2019

Exclusive Hard Processes for Studying Hadron Structures at J-PARC

With an appropriate hard scale, exclusive hadronic processes could provide novel information of the internal quark-gluon configurations of hadrons. The availability of 10-20 GeV secondary meson beam in the coming high-momentum beam line of Hadron Hall at J-PARC offers an unique opportunity to carry out the measurements of the exclusive hard processes. We address this interesting approach by two possibilities: (a) $π^- p \to K^0 Λ(1405)$ for the constituent quark structure of $Λ(1405)$, and (b) exclusive pion-induced Drell-Yan process $π^- p \to γ^* n \to l^+ l^- n$ for the generalized parton distributions (GPDs) of nucleons. Realization of such measurements at J-PARC will open up a new way of accessing the internal quark structure of exotic hadrons and also the nucleon GPDs based on a solid theoretical foundation of perturbative QCD.

nucl-ex↗

arXiv2019

Lepton angular distributions of Drell-Yan process in pQCD and a geometric approach

The lepton angular distributions of the Drell-Yan process in the fixed-target experiments are investigated by NLO and NNLO perturbative QCD. We present the calculated angular parameters $λ$, $μ$, $ν$ and the degree of violation of the Lam-Tung relation, $1-λ-2ν$, for the E615 experiment as well as predictions for the COMPASS experiment. Many salient features of transverse momentum and rapidity dependence could be qualitatively understood by a geometric approach.

hep-ph↗